Mark 15.5 rebreather

I still believe that the Mark 15 is the finest, most engineered, most
tested rebreather in the world, bar none. Mostly due to the
conversations on this list as to why the Mark 15 Series rigs are the
best rigs for everyone to use, and how by simply buying one, you begin
to look like a Greek God with chiselled features that make women swoon
at the sight of you and your manly rebreather, and also the
conversations about how extended use of Cis Lunars, or Inspirations can
cause gonad atrophy, loss of chest hair, sagging buttocks, and a
general repulsion of most members of the opposite sex. So I decided in
the general interest of those who wish to regain their youthful vigour
by investigating thoroughly these magic machines which bestow such
virility on their owners, to publish a list of comparisons of these
magnificent units. All those who read and memorize these pages will find
a new robustness in their demeanour which will bring a twinkle of
anticipatory elation to the eyes of all women they meet, and a knowing
smile from other valorous men who too have heard the Word, and seen
the Way. And those who actually own and dive a Mark 15 Series
Rebreather already know the satisfaction of Crushing their Enemies,
Seeing them Driven Before You, and Hearing the Lamentations of their
Women... Kevin Juergensen

The Golem Flex CCR

Numerous attempts to emulate Rick Stanton's highly successful sidemount CCR have been made by our group. A DDD rebreather was imported and modified by Harry, but faced the issue of gas venting through the unit due the opposing placement of OPV and ADV (OPV on base, ADV on top). JDZ built quite a nice unit from metal but it never saw much action. A bevvy of Satoris where purchased and modified but only Craig had any success diving his, and even that suffered dubious work of breathing due to the bellows counterlung position and design. Grant Pearce made a very workable sidemount KISS that he and Harry dived with some success, but it was somewhat failure prone. So the search for the perfect sidemount unit continued. In March 2012 whislt travelling and diving Florida, Harry thinks he may just have found it. Enter, Jakub Rehacek and his beautifully made GG Flex rebreather...

So after harassing poor Jakub all day at the Rebreather Forum 3 in Orlando, Harry spent the day with Jakub at Ginnie Springs pulling the unit apart and then test diving it before deciding it was just what the Mules were looking for. With a handshake, six units were ordered. Now 6 months later, the first production models are on a plane to Australia and their lucky owners Harry, Grant Pearce, Craig, JDZ, Dave and Sandy.

We have purchased the units in a variety of different configurations. One with Hammerhead displays and DIVA, some with Shearwater displays. Some with sidemount mouth pieces and some with Shrimp BOVs. So we should be able to soon tell you what works and what doesn't, what we love and what might be improved.

Jakub has been awesome to work with, and has taken onboard some feedback already about counterlung size, OPV and ADV locations and fixing points.

Jakub Rehacek chats about the Flex

If the units work as expected, we have big plans for them with upcoming expedition diving in Tasmania, Christmas Island and Camooweal. We will do some tear-downs and reports on the units here as things develop, so watch this space!

Harry testing the Flex

Harry testing the Flex in Ginnie Springs, Florida.

Teardown and first impressions

So the new GG Flex from Golem Gear has arrived and what follows is a teardown and my first impressions of the build quality, form and function of the unit. The Flex is designed primarily as a sidemount rebreather and if successful, will fill a real void in the rebreather marketplace for exploration divers. The term Flex implies flexible, and Jakub intends that this unit could not only be a primary sidemounted unit but might also be used as a secondary Bail out Breather (BOB), or even in the backmounted configuration in a single or twin unit configuration.

As one of the beta testers of the unit, the Flex was sent without any instructions so it was interesting to see how intuitive it would be to put the unit together, and to work out the gas path through the rebreather. Although I had the benefit of diving a prototype in Florida last March, there have been numerous improvements and changes so I was excited to put it together. Once it was done, I did check some details with Jakub so you may be assured that what I have written here is accurate!

So I will start with the unit fully constructed and take it apart showing some of the important features.

Basic Overview

The Flex is slightly wider and slightly taller than an aluminium 11L cylinder. The unit is completely self-contained with the exception of oxygen and diluent gas supplies. It can be ordered with a number of options including the Rev D Hammerhead handsets and DIVA (manual or eCCR), or cables suited to plugging in an external PO2 monitor like the Shearwater or Liquivision X1. An after market HUD like the Shearwater or Narked at 90 can also readily be used. My plan will be for a Shearwater and one of the new rEVO Dreams.

My Flex has been supplied in fully manual configuration with a 0.004” orifice, which should supply 700mls/min of O2 at an IP of 140-150psi. Hence one of the first jobs is to make or source a decompensated O2 1st stage to drive the orifice. I have modified this Poseidon by blocking the ambient port and fixing the IP to 10bar.

In addition to the O2 fed through the “leaky valve”, manual addition of O2 or diluent may occur through the 2 manual add valves provided. An optional Automatic Diluent Valve (ADV) is provided in the inhale counter lung (C/L) and the unit contains two overpressure valves (OPVs) – one in the exhale C/L which has a manual dump, and one in the base of the unit (which can be locked) which doubles as a dump for any water ingress. Spare counter lungs were provided so the OPV and ADV could be omitted if the user prefers.

Build quality

Like all the gear from Golem, the build quality by Jakub’s man in Czechoslovakia is beautiful. A great deal of R&D has clearly gone into this innovative unit and its modular design makes stripping and cleaning the unit a pleasure. The finish on all the delrin components is very good. Golem’s quick disconnect system for hoses and the Bail Out Valve (BOV) always impress me; not only does it work with a positive action but is keyed to prevent incorrect assembly (assuming you put it together the correct way the first time).

Excellent connecting system for the hoses, and very nice right angle adapters for the BOV. You can continue to use a BOV or if you prefer, a sidemount mouthpiece without bailout facility.

The only minor issue I have found relates to the counter lung attachments but more on that later.

Gas path

Starting at the mouthpiece, exhaled gas leaves the mouthpiece and flows down into the top of the unit. Where the supplied Cooper hose enters the head of the unit, a Miflex hose enters the same place with a right angle fitting. This supplies oxygen from the manual add valve, which enters the loop just below the Cooper hose attachment point. This means the O2 must travel through the rest of the circuit before being inhaled, giving plenty of time for adequate mixing before passing over the O2 cells and being breathed.

Gas then enters the exhale C/L immediately below the head. This C/L contains an OPV, which can also be manually activated via a drawstring. After the exhale lung, gas passes through the next bulkhead and down into the outside of the scrubber can, before entering the scrubber from outside in. Any water that has found its way down the exhale side will fall to the bottom of the can and could theoretically be expelled out the lower dump.

In this image the red label marks the expiratory and oxygen side; the white label marks the inspiratory and diluent side.

This image shows the exit point from the exhale C/L at the lower left, with a hint of yellow exhale C/L peeking through. Above that and to the left, the exit point from the O2 "KISS" valve is seen. This is where O2 will be released into the exhale path. Exhaled gas, oxygen from the valve and any water in the loop will drop down this side of the unit into the outer part of the scrubber can.

The hole at the upper right part of the photo is the inhale path from the scrubber up into the pocket containing the cells. This plate is easily removed to expose the 3 fuel cells.

Gas enters the scrubber then passes up the inside of the scrubber to a chamber containing the 3 oxygen cells. The removable cartridge/carrier containing the cells is quite simply the sexiest thing I have ever seen on a rebreather! See the photos and caption for more details.

Plate removed to expose the 3 cells.

Cell carrier on view.

Is that not a beautiful thing? If only all rebreathers had this and we could move our cells from unit to unit!

Past the cells, up into the inhale C/L (which contains the beautifully made ADV), gas then leaves the head via the inhale hose to the diver. Again, at the point where the inhale hose attaches to the head there is another Miflex hose which delivers diluent via the diluent manual add valve. At the head, two other Miflex hoses are seen entering via a radial slot (see earlier image of top of unit). These hoses supply O2 to the KISS-style valve and diluent to the ADV. Two hoses come from the oxygen block (KISS valve and manual add) and two from the diluent block (ADV and manual add). The gas supplies could be configured in a number of ways and supply to both drysuit and wing also needs to be considered. This gets a little more complicated if your diluent cylinder contains helium.

The inhale C/L in situ with the ADV installed. The exhale C/L is absent.

Another sweeeeet feature, the ADV is really nicely made and will activate when the C/L bottoms out. Breathes beautifully.

The "KISS" valve and filter plumbs into the lower bulkhead, and delivers a constant flow of O2 into the exhale side just before the scrubber allowing plenty of time for mixing. On the right, the O2 manual addition valve (MAV) to which I have attached a male QC6 (red). One O2 line (at top of block) is activated by the button (i.e. is manual O2 add) and the other is always open and feeds the "KISS" valve. The diluent side is set up in a similar way.

The Scrubber

The scrubber contains 5.5lbs of sorb (Medium Golem radial scrubber) and is also available in a larger size. The rebreather will become physically that much longer if you choose the larger scrubber, and this will certainly put the base OPV out of reach for most divers.

The scrubber is very easy to fill and has a nice spring-loaded lid that will tamp the sorb down nicely. It is a classic radial design, which should work well. Testing figures for duration are available on the Golem website, and suggest over 2 hours at the usual test paremeters of temperature and CO2 flow. After filling the scrubber, it is placed in the can and the top half of the unit is pushed down into it. The tube below the cells inserts nicely into the top of the scrubber with an O-ring seal. All very nice and simple.

The scrubber plugs in nicely to the base of the rebreather. It is shown here out of its can to demonstrate this.

The Counterlungs

Getting at the C/Ls to clean them is simply a matter of sliding off the upper fenestrated sleeve. A nice locking system makes this a quick thing to do, with no chance of it happening accidentally. Once the sleeve is lifted up and over all the hoses, a clear view of the C/Ls, ADV, OPV, O2 orifice and filter and electronics bulkhead is gained. The 4 attachment points of the counterlungs make for easy removal but I had a little trouble reinserting them without cross threading the plastic. One wonders if this problem will cause damage to the threads over time. The other issue is the silicone washers, which are required at each join, fall out and can be easily lost. Some spares are supplied but some care needs to be taken. I had scattered them around the shed before I realised they were falling out. Leaving a washer out, or cross threading one of the attachments may well cause a failed pressure test or flood the unit.

However, the sytem was designed so the counterlungs do not have to be completely reasembled for day to day cleaning and drying. Just
remove the CL cover and unclip entire
top part from the scrubber can. Remove sensor cartridge. Remove Cooper
hoses. Flush/desinfect C/Ls. Hang the entire assembly by the top handles
to drip dry. So in reality none of this should be an issue.

The OPV in the exhale C/L can be used as a water dump by forcibly exhaling and pulling the string whilst in the appropriate position. This assumes water has not already passed into the base of the scrubber can.

Once the unit is all setup the fenestrated counterlung cover is simply slid down over all the hoses and locked in place.

As easy as 1, 2, 3! Drop the cover on, push the button so the cover drops down then turn until it locks in place. Nice!

Base OPV

The second OPV is on the base of the unit, which can be manually adjusted or set to "lock". Unfortunately early dives suggest the locked setting still allows gas to vent if the base of the unit is too much higher than the head which is a little annoying. A blanking plug is supplied which means the OPV can be removed, but it would be nice to have a vent for any trapped water which could be completely sealed. A stronger spring might be the answer, but anyway Jakub is working on another custom solution to this.

Well that's enough chat, it's time to go dive the thing. Reports are filtering in from the Wetmules and we'll post some first impressions shortly.

I took a while to rig the Flex to ready it for diving. When it is widely available I suggest it should come with a decompensated O2 regulator, some suitable quick disconnects for the MAV blacks and some spares of those silicon O rings!

First Pool Dive

First pool dive yesterday. I noted the following :

ADV in the inhale lung is excellent and works beautifully

Exhale lung OPV good...cracks at an appropriate pressure

Base OPV not satisfactory...even when locked it burps as soon as the arse lifts up and I will be sealing it. This is unfortunate because it would be good to have it as an optional water dump. I found I could get my hand to it OK by pulling the unit up. So I think a dump that is truly locked off, but manually openable for water dumping is needed. I think we have all agreed this is the case.

Positioning and WOB. Like all SM rebreathers I have used it just isn't quite as nice as a more conventional rig however when you do find the sweet spot it is fine. I am using my Armadillo harness, and a 3lb weight on a cam band in the position shown in the early image. This brings the head of the unit up pretty high under my arm. Clipping the top of the unit to my top shoulder D ring worked OK, but what dramatically improved my WOB was subsequently looping my sidemount bungee from the Armadillo around and through the front larger handle on the unit head. This really pulled the top of the unit hard into my armpit.

Hose routing. The O2 side is nice and neat because the hoses are short and sit well on the side of the unit. The O2 button comes nicely to hand in this position, clipped to the side of the unit. The DIL side is not quite as neat. The 2 hoses are of different lengths so don't sit well. I suggest changing the hose carrying manually added DIL to a 35-40cm Miflex (can we get one this length Jakub?), or as Craig suggested, remove the manual add DIL hose and just run the ADV (I was always happy not having a DIL manual add on my KISS so this wouldn't worry me, as long as I have a BOV). This can easily be done by removing the fitting at the head and inserting a 3/8 port plug. The result is a single tidy hose on the DIL side.

Loop hoses. The addition of one SS weight to the short hose, and 2 weights to the longer hose made the loop sit much more comfortably in my mouth. Grant mentioned some discomfort turning his head to the left and certainly I was aware of that if I tried to turn my head, but overall I found it acceptable. Changing to softer hoses as Grant suggested would improve this.

Scrubber. Nice and easy to fill but I found if I filled it to the designated line, I couldn't get the lid on. Is the line a touch high? (N.B. Jake suggests tapping AND rolling the scrubber is required after filling to the line to pack it down properly).

Washing the unit. As Jakub suggested, flushing the whole head assembly (after removing the cell carrier!) is nice and simple and allows inspection of everything without the need to undo those counterlungs. A great feature of the unit. (N.B. I need to check with Jake if it is OK to plunge the whole thing into fresh water knowing that the female side of the cell connectors will be immersed).

O2 bottle. I used a 3L steel and clipped it to the right rear lumbar D ring on the Armadillo. I think I will make an attachment point one level higher and try that, but the O2 cylinder around my legs actually didn't worry me much. A small suit inflator bottle inside the left wing, or in the same fashion as the O2 bottle might be the go for deeper drysuit dives if using diluent not appropriate for suit inflation.

I had a play around with taking off the unit and pushing it ahead of me. It seems pretty well balanced in the water with the 3lb weight on it, however my efforts to streamline the hoses for sidemount diving meant that I had to disconnect everything to swing it freely. I think my procedure will be to never do this except in an emergency, but rather swing my dil cylinder forward when passing tight restrictions. Just too much can go wrong moving the rebreather around at least until I sort some other stuff out.

More soon!Harry

Craig says:

Well I skipped the pool dive and cut straight to an 18m dive yesterday. i have an altogether positive report to make-I am absolutely stoked at how well it went and very excited for its prospects.

Main points:

I too found the ADV was really good. If anything it was a little too light, it might be necessary to isolate it when doing deco, but will see with further diving.

As Harry mentioned I have dispensed with the manual diluent addition to get rid of a hose. I think the ADV is enough, and if I need to add gas otherwise I will use the BOV.

Based on others reports I didn't even bother trying the base OPV, replaced it with the butt plug straight out of the box.

The OPV on the counterlung wouldn't blow off for me, no matter how much I tried. Need to take it apart and see if there is something wrong with it. (It will release if I pull the string).

Had a 4lb weight on the cam band as per Harry's picture With this I found the unit's buoyancy and trim was very similar to the 88 with a 3lb weight on it that I was using on the other side. My position in the water with this setup was really good.

Loop hoses-I am sticking with my around-the-neck setup that I was using with the Sartori, I think it works well. The hoses are both too long at the moment, will have to shorten them but will get to that, it wasn't really of much consequence except they tend to float in front of your face and try and float off. Worse was that the LP hose to my BOV was a bit short and this tended to pull the mouthpiece down and to the left which was annoying, but will fix that also.

The scrubber cannister was bone dry after a 40 minute dive. Life was not like this with the Sartori. Hopefully there will be no need for the water drain at the base.

I could get a good positive pressure test on the unit but the negative pressure test wasn't that great, however it lasted 5-10 minutes which is enough for me, and as mentioned above the unit didn't ship a drop of water during the dive so I'm not too concerned.

Some condensation around the cells, but nothing more than I would normally expect.

In the sweet spot, the breathing was excellent. Obviously if you roll on either side or go head down or head up it is not so great, but still breathable. If I had plenty of gas with me I would probably tend to switch to OC if negotiating restrictions like this, but you could easily get by without doing this if you had to.

The Hammerhead DIVA and handset cables are both way too long. Trying to work out a way to stow the extra length.

Below is a short video of the test. I know all the LP hoses are like a dog's breakfast, I just slapped them together with what I had to hand to get the thing in the water. I've already some up with what I think will be a better solution but will have to wait until next weekend to test now.

With some re-rigging I think I can get the top of the unit higher up into my armpit, which will make the whole setup more streamlined.

You will note from the video that there are no bubbles coming out of it AT ALL, unlike any of my other rebreathers!!!

If the weather holds will try a 50m dive next to make sure it's OK at depth in advance of Tassie

Last night I installed my upgraded rEVO Dream into the unit. This will give me a backup display for two cells and a heads up display which I think is essential for cave diving. The cable is threaded down alongside the yellow Fischer cable and through one of the two available ports. The glands off the Dream fit the thread here perfectly. Turning the unit upside down, the shroud is first removed from the base to expose the female side of the cell carrier plug.

Here we see the shroud that the cell carrier sits in. The shroud accepts inhaled gas from the scrubber into the cell chamber and from there up into the inhale lung.

With the shroud removed, we see how it sits on a beautifully machined area and is o-ring sealed which protects the inhale side from water in the exhale side.

The female side of the cell carrier plug is now visible. A half-circle plate surrounds it but this would not prevent water in this area from moving underneath the carrier plug.

Removing the half circle plate and the cell carrier plug can now be unscrewed and turned over, revealing the wires from the yellow Fischer cable underneath bathed in silicon gel. This could be potted I expect, however that would prevent the addition of further electronics like I am doing. However if you ordered the unit with a full complement of electronics (e.g. the recommended Hammerhead handsets and DIVA), then I would recommend this should be potted (and Golem will routinely provide this).

WIth the half-circle removed, the plug is seen screwed in place. A deep groove runs horizontally underneath this. If that was not present the plug could be seated on an O-ring and make a seal. Is the channel required for machining? (N.B. Jakub advises this was a conscious decision so as not to form an area that would be exposed to ambient pressure, and hence risk imploding).

The smile shaped groove on the left is for solenoid wiring.

The plug can be lifted up and turned over to reveal the 3-common earths and 3 separate active sensor wires, which contain a small resistor at their terminus.

The reverse of the plug was filled with silicon gel but could be potted as one way of protecting these connections from water. If the entire head was dunked in water to wash it (which is a very attractive idea), water could potentially make its way into here.

Anyway the Dream is in, and my first ocean dives this weekend!

Harry

Flex at Glenelg

Here is some footage from my first ocean dives yesterday.

Tasmanian Cave Diving Expedition - Flexes in action!

Four of the Wetmules have just returned from a trip to Tasmania, where they dived the Junee Resurgence in the Junnee-Florentine karst near the Mt Field National Park. This streamway cave has been explored by cave divers since the 60's but progress had stalled when Tim Payne and David Doolette came up against a rockpile collapse in the second sump several years ago. In 2009 JDZ and Harry dived the second sump, hoping to find a way through that other divers had missed. This was not successful so we hoped that with the benefit of sidemount CCR it might be worth one more try, especially with the theoretical lure of several kilometres of tunnel on the other side.

The cave exists as two sumps separated by a beautiful streamway passage called For Your Eyes Only (FYEO). The water is about 7 degrees Celcius, moderate flow and low viz (1-4m). The passage is very silty and restricted in parts...perfect country for testing the new Flex units! Once into FYEO, it takes 20 minutes to walk dive gear up to the start of the second sump along the stream way, over a couple of small waterfalls. The second sump descends to 66m depth before rising slightly towards the rock pile which currently obstructs further exploration. The limestone throughout the cave is sharp and harsh on drysuits and other gear, and the grit and silt gets into everything! Second stages constantly play up and the Flexes needed o be stripped down every couple of days to clear the sediment from them.

Sandy, Dave and Craig strip down the Flex rebreathers in Tassie to remove the large amounts of cave sediment which was getting into the units. All our dive gear was misbehaving a bit, not just the rebreathers.

In total the group performed 52 dives on the breathers in the very tough conditions. We also met up with Grant Pearce who had been diving his Flex nearby. The trip was an excellent opportunity for some concentrated R&D and we spoke to Jakub several times during the week to give him updates and give feedback. I have to say Jake is very receptive to critical feedback and welcomed all our comments both good and bad.

Two major issues with the units became apparent. The counterlungs occasionally fold over their openings and limit or obstruct respiration. We didn't detect this on the open water test dives, but in the restrictive cave with variable head up and down attitudes, this problem came to light. An easy fix will be to install some kind of cage or spacer inside the lung or over the openings to the lungs. The second problem occured with the ADV. On occasions the ADV provided insufficient gas during inspiration. We think this was also due to an issue with the inspiratory lung folding into a shape that wouldn't trigger the ADV correctly. A flat firm backing on the opposite wall of the lung might fix this. The same ADV is used on the OTS lung on the Hammerhead unit and it is very successful there.

When sitting in the water gearing up, the ADV will fire continuously if the mouthpiece is open. This is a common characteristic of sidemount rebreathers and relates to the hydrostatic pressure on the ADV compared to the open DSV, However on a few occasions we had trouble with a free flowing ADV over pressurising the loop during a dive, especially on ascent. This made the unit unbreathable. The ADV may need to be detuned a little to overcome this, but again Jake is on the case to sort this out.

Overall our experience with the units was a very positive one. We believe once these couple of faults are sorted, the Flex is going to be a serious tool for exploration. At 65m swimming into flow in 7 degree water the unit breathed very well and made for streamline exploration. Trim on the unit is much like diving open circuit side mount and is an absolute delight.

Stripping down the unit is extremely simple and washing it is a joy. Some buildup of grit can make removing the fenestrated counterlung cover hard to do, so Jakub is thinking about how to improve this. This is important as the unit will often be used in tight and dirty caves.

Another aspect that impressed us was the robust nature of the unit. Cavers are not kind to dive gear, and we skull dragged these units up and down the streamway passage for a week, using them as walking sticks to balance on rocks and banging them hard on a regular basis. I would not like to treat my back mounted units in this way!

We spent a large amount of time fine tuning the loop and LP hose lengths, tried diving with and without the ADV and dil manual add blocks, and we will pass on our recommendations to Jake so that hopefully he can provide tailored solutions to buyers in future. We all agree that having the loop hoses around our neck worked best for a number of reasons. The BOV sits comfortably in your mouth using straight connectors into the BOV (as opposed to the right angled ones supplied). Passing through tight passage risks the loop being pulled from your mouth; and having it around your neck means it cannot be lost underneath you. The tough Cooper hoses sit in the nape of your neck and do not rub on the roof of the cave. A good quality BOV is essential with this kind of diving in our opinion.

Junee 2013

Low pressure hose configuration - one suggestion

Sorting out loop hoses and low pressure hoses has been a bit of a challenge and needs may vary from diver to diver. I am not sure if Jakub has finalised how he will offer the hoses. Most of our group have decided on having the loop around our neck, but we are still experimenting with all the other hoses. I think Mr Miflex must be very happy with us! Below are 2 images showing the way I am currently trying to make things as streamlined as possible. One photo shows the regulator from the (left) sidemounted diluent cylinder. This is usually a steel 12L or aluminium 11.8L tank. The second image shows the diluent side on the rebreather. The manual add button clips to my left shoulder D-ring. A very short Miflex hose feeds the BOV on the Shrimp. The sliding shut off valve can isolate the ADV but I hope to remove this once some teething issues with the ADV are resolved. The hose with the female QC6 comes under my left arm to the male QC6 from the rebreather...all nice and neat. The right angle on the male QC6 is needed to route the hose under my left armpit.

Spot the "intentional" mistake? The ADV and manual add hoses are in the wrong holes of the manual add valve!

You'll note at present I only have a hose for my drysuit inflation, or wing inflation. If I start doing deeper sinkhole or wreck dives on this unit I will add another hose, but for now I am happy with just one for the types of dives I am doing. Harry.

October 2013 Update

A considerable number of dives have been done by the group now, to a maximum depth of nearly 130m. There is almost universal acceptance of the 'round the neck" loop approach with one long hose (940cm) behind the neck, and one short soft Drager Ray hose from the unit to the Golem Shrimp BOV. I have alsoi been doing a few dives using the sidemount mputhpiece made for me by Forrest Wilson, and Grant uses his Airtess. With this configuration I use two Drager Ray hoses and find this very comfortable. This means no HUD and only one wrist display so I only go this way if I have no alternative (e.g. using it as a bailout unit).

I think all 6 of us have had a problem with the leaky valve becoming obstructed with rust particles. I assume this means a drop of water is finding its way through the QC6 connectors and because the filter-valve assembly sits vertically, it must sit above the orifice and generate rust. So I have discarded this component and added a KISS valve (which conveniently combines the manual add with the leaky valve and so gets rid of yet another hose). Apologies for crappy i-phone photo but this is shown below.

The new heads which contain the ADV should solve the problem of the ADV not working in the lung intermittently, but most of us are not using the ADV much now anyway exceot when the unit is a bailout. The OPV has the string removed now and will handle severe overpressure when ascending off the unit...otherwise we just burp gas from our mouth on ascent.